<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
  .content {
    width: 180px;
    height: 64px;
    margin: 0;
    padding: 0;
    border: none;
    background: transparent;
    position: relative;
    font-size: 24px;
  }
  .content::before {
    content: '';
    position: absolute;
    top: -2px; bottom: -2px;
    left: -2px; right: -2px;
    background: olivedrab;
    border: 2px solid olive;
    z-index: -1;
  }
  </style>
</head>
<body>
  <button class="content">我是内容</button>
</body>
</html>